Garage Heater Running Costs

We deliberately publish consumption rather than dollar costs. US electricity rates vary by roughly a factor of three between states and change annually, and natural gas rates vary seasonally — so any dollar figure typed into a page is wrong somewhere and wrong everywhere eventually. The consumption numbers above are fixed physics. One multiplication by your own rate gives you an answer that is actually correct.

Do the arithmetic yourself, in two steps

Electric

1. Take the wattage and divide by 1,000 to get kWh per hour. A 5,000W heater is 5 kWh per hour.
2. Multiply by your rate per kWh, which is on your electricity bill.

That is the full cost, because electric resistance heat is 100% efficient at the heater — there is no conversion loss to account for.

Natural gas

1. Take the output BTU and divide by the efficiency. The Modine's 45,000 BTU output at 80% means 56,250 BTU of gas input per hour.
2. Divide by 100,000 to get therms (1 therm = 100,000 BTU). That is 0.5625 therms per hour.
3. Multiply by your rate per therm, which is on your gas bill.

In most of the US that calculation produces a figure substantially below the electric equivalent for the same heat, which is the entire argument for gas.

Propane

1. A 20 lb cylinder holds roughly 430,000 BTU.
2. Divide by the heater's BTU rating for hours of continuous running. 430,000 ÷ 60,000 is about 7 hours.
3. Divide the cylinder refill price by those hours.

Comparing fuels at the same heat output

The fairest comparison is energy consumed to deliver the same heat. Take 25,590 BTU per hour — TEMPWARE's published figure for its 7,500W electric heater:

• Electric — 7.5 kWh of electricity.
• Natural gas at 80% — 32,000 BTU of gas input, which is 0.32 therms.
• Natural gas at 83% — 30,800 BTU, which is 0.308 therms.

Put your own rates against those three numbers. In most US markets the gas figures come out well under the electric one, and that gap is why a gas install pays back over a winter of regular use — and why it does not pay back if you heat the garage six times a year.

Three things that cut running cost more than fuel choice

1. Insulation

The biggest lever by a wide margin. An uninsulated garage needs roughly twice the heater and runs it roughly twice as long as an insulated one — see the columns in the garage heater sizing guide.

The garage door is usually the single biggest hole: a large uninsulated panel with gaps around the perimeter. Insulating and sealing it costs less than the difference in heater size and pays back every hour the heater runs. How to insulate a garage for heating.

2. A lower setpoint, and a lower output level

Heat output scales with the temperature difference you are maintaining. Holding 55°F instead of 68°F in a 20°F outdoor climate cuts the load by roughly a quarter.

Multi-level heaters make this practical: Mr. Heater's 2VAHG5000 runs at 3,000W as well as 5,000W, so a mild day costs 40% less than a cold one. A single-output heater cannot do that. InoKraft's 40°F minimum thermostat setting is specifically designed for 'keep it above freezing and nothing more'.

3. Heat the person, not the building

If you work at a bench for an hour, a 1,500W infrared heater aimed at where you stand costs 1.5 kWh. Heating the whole 450 sq ft garage to comfort costs 5-7.5 kWh for the same hour of work.

That is a four-to-five-fold difference, and it is the strongest argument for owning a 120V comfort heater ALONGSIDE a proper garage heater rather than instead of one. Use the big one when you need the space warm; use the small one when you just need to be warm.

What about a heat pump?

A mini-split moves heat rather than generating it, so it delivers several units of heat per unit of electricity — which makes it cheaper to run than any resistance heater and competitive with gas.

Two caveats that keep it off the table above. Its efficiency falls as it gets colder, exactly when you want output. And it only works properly in an insulated, sealed garage. Full discussion on garage heater vs mini-split.

The low-running-cost options

Next

If the arithmetic has pushed you toward gas, the best natural gas garage heaters covers the models and what the vent install needs. If it has pushed you toward spending less on heat altogether, is a garage heater worth it is the honest version of that question.